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Re: SG-239 Tuning Problem

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  • beltran_thomas
    I have a question about counterpoises - I plan on using an SG-231 on a balcony with the antenna wire (23 feet long) attached to a near-by tree. I am on the
    Message 1 of 21 , Apr 3 9:27 AM
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      I have a question about counterpoises - I plan on using an SG-231 on a
      balcony with the antenna wire (23 feet long) attached to a near-by
      tree. I am on the ground-floor, which, because of the underground
      parking puts me about 6 feet off the ground. Does the counterpoise
      need to be tuned? The examples in the SGC manual all show random
      length radials, but they are directly on the ground or in water.
      Thanks in advance. Tom

      --- In Smartuners@yahoogroups.com, "David H Hatch" <dhatch@...> wrote:
      >

      I have
      > used live trees as counterpoises; aluminum canoes as antennas; tried
      liquid
      > antennas; jumper cables as antennas with an aluminum garage door as
      the
      > counterpoise. Try a cyclone ball diamond as a counterpoise and a long
      wire
      > stretched out over home base as the antenna - it will work. I have
      > countless stories, and great memories in experimenting with these.
      Just
      > follow the simple guidelines. The SGC manuals have been my Elmers, as
      have
      > those who wrote them.
    • Jed Petrovich
      David: My apologies... for some reason, I didn t see your messages until a few minutes ago. So it s now about midday on Tuesday, April 3rd as I m writing this.
      Message 2 of 21 , Apr 3 9:54 AM
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        David:

        My apologies... for some reason, I didn't see your messages until a few minutes ago. So it's now about midday on Tuesday, April 3rd as I'm writing this.

        My dipole is about 130' end to end. This means each side is 65' in length. Again, it's fed with 450 ladder line.

        As an update, the 239 is on it's way back to SGC so they can have a look at it. One of the techs at SGC had me run some tests using the light bulb "dummy load". After the testing, I made another call and we both decided it sounded like the tuner needed some attention. The tuner should arrive at SGC tomorrow, but I don't know how long it will take for them to test/fix the unit and send it back.

        Thanks for your response to my post...

        Jed

        On 3/30/07, David H Hatch <dhatch@...> wrote:

        Hi again Jed,

         

        Your description says your dipole is 130'. Note the specs for the unit….

         

        http://www.sgcworld.com/239ProductPage.html

         

        Minimum lengths:

        40 feet (3.3 to 30 MHz)  

        100 feet (1.8 to 30 MHz)

         

        That would be 100' on the RF-Hot side for 1.8 to 30 MHz, if I recall right.

         

        Dave


      • David H Hatch
        Tom said. I have a question about counterpoises - I plan on using an SG-231 on a balcony with the antenna wire (23 feet long) attached to a near-by tree. I am
        Message 3 of 21 , Apr 3 8:29 PM
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          Tom said…

           

          “I have a question about counterpoises - I plan on using an SG-231 on a
          balcony with the antenna wire (23 feet long) attached to a near-by
          tree. I am on the ground-floor, which, because of the underground
          parking puts me about 6 feet off the ground. Does the counterpoise
          need to be tuned? The examples in the SGC manual all show random
          length radials, but they are directly on the ground or in water.
          Thanks in advance. Tom”

          Dave-N9ZRT replies…

           

          Hi Tom, the counterpoise does not have to be tuned, or cut to length. Just have it somewhat longer than the antenna. You can lay it out on the lawn, that will work fine, or drop it down from the balcony. The important thing is that the counterpoise is longer, or “electrically larger” than the antenna. The coupler will see it, and it will smile. So will the operator. J

           

          Dave

           

        • David H Hatch
          Jed wrote. My dipole is about 130 end to end. This means each side is 65 in length. Again, it s fed with 450 ladder line. As an update, the 239 is on it s
          Message 4 of 21 , Apr 3 8:40 PM
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            Jed wrote…

             

            “My dipole is about 130' end to end. This means each side is 65' in length. Again, it's fed with 450 ladder line.

            As an update, the 239 is on it's way back to SGC so they can have a look at it. One of the techs at SGC had me run some tests using the light bulb "dummy load". After the testing, I made another call and we both decided it sounded like the tuner needed some attention. The tuner should arrive at SGC tomorrow, but I don't know how long it will take for them to test/fix the unit and send it back.”

             

            Dave-N9ZRT replies…

             

            Jed and the group, I spend considerable time with an engineer from SGC at the AES Superfest on Saturday. I got clarification on some things. Regarding antenna lengths, take a look at the front of the SG-239…

             

            http://www.universal-radio.com/CATALOG/hamtune/1401spec.jpg

             

            Specifically, the “antenna length” is the RF-Hot side only, not end to end of a dipole. So, for the SG-239 to work 160 meters on a DIPOLE, the RF-Hot side would be greater than or equal to 100 feet, while the RF-GRN side would be another 100+ feet. The dipole would be over 200 feet long, end to end. For shorter wavelengths, the antenna would be shorter, as per the cover of the SG-239. Perhaps this is helpful.

             

            I hope your coupler comes back working like a trooper.

             

            Dave-N9ZRT

             

             

             

          • Randy Charles Ford
            ... Any idea if a 100 ft folded dipole would work? 73, Randy - KG4JIX
            Message 5 of 21 , Apr 3 11:01 PM
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              On Tuesday 03 April 2007 10:40 pm, David H Hatch wrote:
              > Specifically, the "antenna length" is the RF-Hot side only, not end
              > to end of a dipole. So, for the SG-239 to work 160 meters on a
              > DIPOLE, the RF-Hot side would be greater than or equal to 100 feet,
              > while the RF-GRN side would be another 100+ feet. The dipole would be
              > over 200 feet long, end to end. For shorter wavelengths, the antenna
              > would be shorter, as per the cover of the SG-239. Perhaps this is
              > helpful.

              Any idea if a 100 ft folded dipole would work?

              73, Randy - KG4JIX
            • David H Hatch
              Randy wrote. Any idea if a 100 ft folded dipole would work? N9ZRT replies. Good morning Randy. I believe the same rule would apply with a folded dipole, that
              Message 6 of 21 , Apr 4 3:20 AM
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                Randy wrote…

                 

                “Any idea if a 100 ft folded dipole would work?”

                 

                N9ZRT replies… Good morning Randy. I believe the same rule would apply with a folded dipole, that is:

                 

                • Using the guide on the face of the SG-239 when it comes to all antennas [including dipoles], the length described for the various bands, is the RF-Hot side.
                • So, to work 160 meters on the SG-239, the RF-Hot side needs to be 100’, the counterpoise a touch longer. Randy, I will take your sentence above and edit it as follows…

                 

                “Any idea if a folded dipole [with a 100’ length on the RF-Hot side and 100+ feet on the RF-GRN side] would work?”

                 

                Dave replies… Yes, according to the manual, that should work.

                 

                Hoping this was helpful, Randy.

                 

                Dave-N9ZRT

                 

              • Graham Ridgeway
                On Wed, 4 Apr 2007 01:01:03 -0500, Randy Charles Ford ... It would look like a squashed loop to the 239 73 Graham M5AAV
                Message 7 of 21 , Apr 4 3:30 AM
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                  On Wed, 4 Apr 2007 01:01:03 -0500, Randy Charles Ford
                  <kg4jix@...> wrote:

                  >On Tuesday 03 April 2007 10:40 pm, David H Hatch wrote:
                  >> Specifically, the "antenna length" is the RF-Hot side only, not end
                  >> to end of a dipole. So, for the SG-239 to work 160 meters on a
                  >> DIPOLE, the RF-Hot side would be greater than or equal to 100 feet,
                  >> while the RF-GRN side would be another 100+ feet. The dipole would be
                  >> over 200 feet long, end to end. For shorter wavelengths, the antenna
                  >> would be shorter, as per the cover of the SG-239. Perhaps this is
                  >> helpful.
                  >
                  >Any idea if a 100 ft folded dipole would work?
                  >

                  It would look like a 'squashed loop' to the 239



                  73 Graham M5AAV
                • David H Hatch
                  Hi Graham, Your words. It would look like a squashed loop to the 239 Daved-N9ZRT replies, From my thinking, more so, it may look like a squashed loop to
                  Message 8 of 21 , Apr 4 3:51 AM
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                    Hi Graham,

                     

                    Your words… “It would look like a 'squashed loop' to the 239”

                     

                    Daved-N9ZRT replies,

                     

                    From my thinking, more so, it may look like a squashed loop to the passerbys below looking up, but to the coupler, it would still be a dipole, as the antenna does not connect from the RF-Hot lug to the RF-GRN lug.

                     

                    I believe, if the space between the folded wires were too close, the coupler could see it as half of the wire’s length [That is, the wire’s folded length], so the gap between the folded wire would have a minimum.

                     

                    Your thoughts on this?

                     

                    One cup of expresso down, more to go. Muddy!

                     

                    Dave

                     


                    From: Smartuners@yahoogroups.com [mailto:Smartuners@yahoogroups.com] On Behalf Of Graham Ridgeway
                    Sent
                    : Wednesday, April 04, 2007 5:30 AM
                    To: Smartuners@yahoogroups.com
                    Subject: Re: [Smartuners] SG-239 Tuning Problem

                     

                    On Wed, 4 Apr 2007 01:01:03 -0500, Randy Charles Ford
                    <kg4jix@...> wrote:

                    >On Tuesday 03 April 2007 10:40 pm, David H Hatch wrote:
                    >> Specifically, the "antenna length" is the RF-Hot side only,
                    not end
                    >> to end of a dipole. So, for the SG-239 to work 160 meters on a
                    >> DIPOLE, the RF-Hot side would be greater than or equal to 100 feet
                    class=GramE>,
                    >> while the RF-GRN side would be another 100+ feet. The dipole would be
                    >> over 200 feet long, end to end. For shorter wavelengths, the antenna
                    >> would be shorter, as per the cover of the SG-239. Perhaps this is
                    >> helpful.
                    >
                    >Any idea if a 100 ft folded dipole would work?
                    >

                    It would look like a 'squashed loop' to the 239

                    73 Graham M5AAV

                  • Randy Charles Ford
                    ... I m refering to a folded dipole without any gaps. It is electrically one wire that connects between RF-HOT and RF-GRN. ... RF-HOT-^ ^-RF-GND 73, Randy -
                    Message 9 of 21 , Apr 4 4:59 AM
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                      On Wednesday 04 April 2007 05:51 am, David H Hatch wrote:
                      > Hi Graham,
                      >
                      > Your words. "It would look like a 'squashed loop' to the 239"
                      >
                      > Daved-N9ZRT replies,
                      >
                      > From my thinking, more so, it may look like a squashed loop to the
                      > passerbys below looking up, but to the coupler, it would still be a
                      > dipole, as the antenna does not connect from the RF-Hot lug to the
                      > RF-GRN lug.
                      >
                      > I believe, if the space between the folded wires were too close, the
                      > coupler could see it as half of the wire's length [That is, the
                      > wire's folded length], so the gap between the folded wire would have
                      > a minimum.
                      >
                      > Your thoughts on this?
                      >
                      > One cup of expresso down, more to go. Muddy!
                      >
                      > Dave

                      I'm refering to a folded dipole without any gaps. It is electrically
                      one wire that connects between RF-HOT and RF-GRN.

                      ___________________________________
                      |_______________ _______________|
                      | |
                      RF-HOT-^ ^-RF-GND

                      73, Randy - KG4JIX
                    • David H. Hatch
                      Hi Randy, You mention, I m referring to a folded dipole without any gaps. It is electrically one wire that connects between RF-HOT and RF-GRN. Gottcha. That
                      Message 10 of 21 , Apr 4 7:13 AM
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                        Hi Randy,

                         

                        You mention, “I'm referring to a folded dipole without any gaps. It is electrically
                        one wire that connects between RF-HOT and RF-GRN.”

                         

                        Gottcha. That would then be a loop antenna, I believe, squashed, but a loop. I like that name, “Squashed Loop”.

                         

                        Snow here – Green Bay , Wisconsin .

                         

                        Dave-N9ZRT

                      • Jed Petrovich
                        Dave: Thanks for the information about the antenna lengths. Since my dipole is only 130 total, I haven t even tried working any 160m. It seems to work pretty
                        Message 11 of 21 , Apr 4 9:22 AM
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                          Dave:

                          Thanks for the information about the antenna lengths. Since my dipole is only 130' total, I haven't even tried working any 160m. It seems to work pretty well on 10 - 80m. It does make sense that the "length" would only be one side of a dipole. From what I remember, the documentation isn't very clear on this.

                          Likewise, I'm hoping the problem with my tuner can be resolved. I've borrowed a little manual tuner so I can do a little work, but I sure miss my 239.

                          Jed

                          On 4/4/07, David H. Hatch <dhatch@...> wrote:

                          Hi Randy,

                           

                          You mention, "I'm referring to a folded dipole without any gaps. It is electrically
                          one wire that connects between RF-HOT and RF-GRN."

                           

                          Gottcha. That would then be a loop antenna, I believe, squashed, but a loop. I like that name, "Squashed Loop".

                           

                          Snow here – Green Bay, Wisconsin.

                           

                          Dave-N9ZRT


                        • Graham Ridgeway
                          On Wed, 4 Apr 2007 09:13:44 -0500, David H. Hatch ... Wall to Wall Clear blue skies here - around 17 deg C but cold at altitude - nice vapour trails at
                          Message 12 of 21 , Apr 4 10:00 AM
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                            On Wed, 4 Apr 2007 09:13:44 -0500, "David H. Hatch"
                            <dhatch@...> wrote:

                            >Hi Randy,
                            >
                            >You mention, "I'm referring to a folded dipole without any gaps. It is
                            >electrically
                            >one wire that connects between RF-HOT and RF-GRN."
                            >
                            >Gottcha. That would then be a loop antenna, I believe, squashed, but a loop.
                            >I like that name, "Squashed Loop".
                            >
                            >Snow here - Green Bay, Wisconsin.

                            Wall to Wall Clear blue skies here - around 17 deg C but cold at
                            altitude - nice vapour trails at Angels 20 plus - Lancashire UK

                            However. A folded diple does have no 'gaps' so is a modified loop,
                            with [conventionally] a feed point impedance of 300R, but that of
                            course varies dependant on the wire spacing.
                            One has to saythat in theory it will work - but then going on what I
                            attach to my 239 and MACS [which are 239's in all but name] theory
                            goes out of the window 90% of the time !

                            Try it and amaze yourself


                            73 Graham M5AAV
                          • David H Hatch
                            Graham, send the WX over. Not recalling the counterpoise, my SG-239 found a fast match on 80 meters using my 17 foot aluminum [Grumman] canoe as the antenna.
                            Message 13 of 21 , Apr 4 10:23 AM
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                              Graham, send the WX over.

                               

                              Not recalling the counterpoise, my SG-239 found a fast match on 80 meters using my 17 foot aluminum [Grumman] canoe as the antenna. Yes, the canoe was out of the water. I think the huge aluminum surface area made the 17 footer very broad banded. Did I make a contact? Not that time, but other times, when mobile with the canoe, I did.

                               

                              At the AES Superfest, four folks gathered around an SG-239, held hands, with the two end-hands touching the two lugs [RF-Hot and RF-GRN], and pretended to be a giant loop. Much fun had at a booth, these things done to show the simplicity of the device.

                               

                              Dave-N9ZRT

                               

                              [About to do the funeral service here for WB9EWK-Tom SK, age 56]

                            • Robert WE4B
                              Tom, I ve had a local ham in the same situation as you, except he is on the 26th floor of a condo on Miami Beach. I made him my special SGC STEALTH CONDO
                              Message 14 of 21 , Apr 4 11:20 AM
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                                Tom,

                                I've had a local ham in the same situation as you, except he is on the 26th floor of a condo
                                on Miami Beach. I made him my special SGC STEALTH CONDO ANTENNA. This is how I did
                                it. I used an MFJ fiberglass pole (32' long), a potted planter (Big one with dirt and an SGC
                                230 tuner planted inside with a nice Philodendron, a 22 gauge wire counterpoise all
                                around the base edge on the floor of the balcony. I then made a pvc rig that would allow
                                him to rest the pole on the bannister along the edge of the balcony railing. but when he
                                wanted to use it he would swing it out away from the building. He could adjust it enough
                                to give him North/South and Northwest/Southeast in direction. On the fiberglass pole I
                                removed the tip extenuation which shortened the length to 30 feet. I then epoxy the
                                connections between each section so it would no longer collapse, I then used the
                                WIREMAN 26 Gauge black coated antenna wire and epoxied the end to the hole in the tip,
                                and the laid it along the top of the pole and epoxied it to the pole. Then I made the PVC
                                connection to the inside on the pole at the base and down to a PVC plate that the planter
                                sat on.
                                So here is how it works for him. When he wants to operate he walks outside, swings the
                                pole Horizontally off the side of the building off where it was resting on the railing of the
                                balcony, takes the coax and 12v line inside to his station and closes the sliding door. He
                                connects it up to the radio and 12V and he is on the air. He loves it and has worked DXCC
                                with it, and also like that he is able to hide it when not using it. So his counterpoise Tom is
                                a wire 120 foot rectangle around the edge along the floor which works great. I've made a
                                few of these for hams on condo, even one that used 2 Shakespeare 390's marine antenna's
                                (23 foot white fiberglass (very heavy)) one as a counterpoise.
                                I'm sure that a counterpoise around the floor of your balcony will work fine.
                              • w8fn1
                                ... end to end ... the RF-Hot ... side would ... to end. ***RF Engineer hat going on*** Although it is a practical spec, the spec regarding required antenna
                                Message 15 of 21 , Apr 4 12:16 PM
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                                  > Specifically, the "antenna length" is the RF-Hot side only, not
                                  end to end
                                  > of a dipole. So, for the SG-239 to work 160 meters on a DIPOLE,
                                  the RF-Hot
                                  > side would be greater than or equal to 100 feet, while the RF-GRN
                                  side would
                                  > be another 100+ feet. The dipole would be over 200 feet long, end
                                  to end.

                                  ***RF Engineer hat going on***

                                  Although it is a "practical" spec, the spec regarding required
                                  antenna lengths for the SGC couplers is somewhat incomplete, and
                                  possibly misleading. I'm basing the following on an analysis of the
                                  innards of the SG-230. Unless the circuit topology is radically
                                  different in the SG-239 and others, the same comments should apply
                                  equally.

                                  If you look at the circuit of the matching network of the SG-230 as
                                  presented in the schematics in the manual, you'll see that what we
                                  have in the box is an adjustable unbalanced low-pass network that
                                  can be configured either as a Pi network or as one of two types of L
                                  network (capacitor on the load side or capacitor on the source
                                  side), depending on the solution the tuning algorithm arrives at.
                                  The RF input from the radio is applied between one end of the tuning
                                  network and circuit "Ground" (Common), which is also the common
                                  return for power and control signals. The "hot" output side of the
                                  matching network connects to the antenna post and the counterpoise
                                  connection (in the case of the SG-230, the stud at the bottom of the
                                  case) connects back to RF / power common via a pair of
                                  paralleled .033uF capacitors in parallel with a 220K 1W resistor.
                                  For any frequency in the range of the tuner, these paralleled
                                  capacitors amount to a dead short. This technique is clearly
                                  implemented to break the DC connection between the counterpoise and
                                  the return back to the power supply so that whatever is used as a
                                  counterpoise in the normal random-wire matching scenario can't
                                  produce sneak paths back to power ground. This is the same type of
                                  ground isolation technique that was used in the old hot-chassis
                                  transformerless tube radios and TVs from days gone by. At RF,
                                  however, the control and power lines CAN be very much a part of the
                                  RF return circuit, and therefore part of the antenna. It's never
                                  been clear to me why the SGC designers didn't complete the job of
                                  isolating the RF and power/control returns by simply putting small
                                  chokes in the non-RF lines, but they didn't.

                                  For any load connected to the output of the matching network, RF
                                  current flowing "out" the antenna port WILL flow "back" into the
                                  counterpoise port, and the majority of the return current will take
                                  whichever path presents the lowest impedance. If the tuner is being
                                  used to match a random wire it is important that the vast majority
                                  of the return side RF current be forced to find its way back to the
                                  low side of the matching network through some path that has a stable
                                  and significantly lower impedance than the power/control lines.
                                  Hence the requirement for a sizable counterpoise to insure matching
                                  stability and minimize "RF in the shack" problems.

                                  For the case of a loop or a dipole (or more properly, a doublet),
                                  which are (more or less) balanced loads across the matching network
                                  output, the current out of the antenna port will return pretty much
                                  completely in a closed loop via the other side of the feedline to
                                  the counterpoise port. Barring large amounts of pickup from the
                                  control lines being in the near field of the antenna, the control
                                  lines are essentially out of the picture as part of the RF return
                                  path. This is of course an oversimpification, as many factors can
                                  upset the balance of the antenna, but as a first-order approximation
                                  it is good enough. Feeding a doublet a small distance away from its
                                  center will neither change the current distribution on the antenna
                                  nor appreciably affect the current balance at the feed point; it
                                  just changes the feedpoint impedance. This is the principle used in
                                  the various "Windom" off-center fed designs.

                                  When feeding a doublet or loop via a length of some kind of
                                  feedline, the load the matching network has to deal with will be
                                  determined by the feedpoint impedance of the antenna as transformed
                                  through the feedline. If the matching network can be adjusted to
                                  transform the resulting complex impedance to a nominal 50 Ohms
                                  resistive at the operating frequency, the system will be happy
                                  irrespective of whether the feedpoint of a doublet is exactly at the
                                  center or not.

                                  The real question of whether or not a particular antenna will match
                                  successfully is whether the tuner is capable of matching the load
                                  the antenna system (including feedline) presents at its output
                                  terminals, not the exact geometry of the antenna. The matching range
                                  of the tuner is determined by the adjustable network constants
                                  available. Since electrically short antennas are highly capacitive
                                  loads, as a first approximation the matching capability of a lowpass
                                  tuner topology such as that used in the SGC designs for short wires
                                  can be inferred by the maximum inductance available. That's why the
                                  physically larger (and more expensive) tuners can match shorter
                                  wires at a given frequency.

                                  There are other constraints as well. Although the tuner may be
                                  capable of finding a setup that transforms a given impedance to 50
                                  Ohms, it may well be that RF currents and voltages at various points
                                  in the matching network can reach values capable of damaging its
                                  components, even at power levels well below its nominal rating. For
                                  example, if you find an autotuner trying to retune itself after a
                                  few seconds of high-duty cycle transmission, you're probably seeing
                                  the detrimental effects of RF heating in one or more of the network
                                  capacitors.

                                  The bottom line is that the design used by the SGC tuners does NOT
                                  require a particular "magical" antenna arrangement to work properly.
                                  They work just fine feeding doublets as well as end-fed wires. I
                                  have had great success feeding a 102' doublet via a length of 450
                                  Ohm ladder line. Depending on the exact geometry, it may be
                                  necessary to fool around with the feedline length to achieve a match
                                  on all desired frequencies. The SGC folks are right in discouraging
                                  the use of coax as a feedline for this kind of antenna. Coax is way
                                  too lossy at the high VSWRs that are inherent in this kind of
                                  service. Stick with a low-loss feedline and you'll find it works
                                  quite well.

                                  73...
                                  Randy, W8FN
                                • David H Hatch
                                  Great input, Randy! Thanks! Dave-N9ZRT _____ From: Smartuners@yahoogroups.com [mailto:Smartuners@yahoogroups.com] On Behalf Of w8fn1 Sent: Wednesday, April 04,
                                  Message 16 of 21 , Apr 4 5:36 PM
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                                    Great input, Randy!

                                     

                                    Thanks!

                                     

                                    Dave-N9ZRT

                                     


                                    From: Smartuners@yahoogroups.com [mailto:Smartuners@yahoogroups.com] On Behalf Of w8fn1
                                    Sent: Wednesday, April 04, 2007 2:17 PM
                                    To: Smartuners@yahoogroups.com
                                    Subject: [Smartuners] Re: SG-239 Tuning Problem

                                     


                                    > Specifically, the "antenna length" is the RF-Hot side only, not
                                    end to end
                                    > of a dipole. So, for the SG-239 to work 160 meters on a DIPOLE,
                                    the RF-Hot
                                    > side would be greater than or equal to 100 feet, while the RF-GRN
                                    side would
                                    > be another 100+ feet. The dipole would be over 200 feet long, end
                                    to end.

                                    ***RF Engineer hat going on***

                                    Although it is a "practical" spec, the spec regarding required
                                    antenna lengths for the SGC couplers is somewhat incomplete, and
                                    possibly misleading. I'm basing the following on an analysis of the
                                    innards of the SG-230. Unless the circuit topology is radically
                                    different in the SG-239 and others, the same comments should apply
                                    equally.

                                    If you look at the circuit of the matching network of the SG-230 as
                                    presented in the schematics in the manual, you'll see that what we
                                    have in the box is an adjustable unbalanced low-pass network that
                                    can be configured either as a Pi network or as one of two types of L
                                    network (capacitor on the load side or capacitor on the source
                                    side), depending on the solution the tuning algorithm arrives at.
                                    The RF input from the radio is applied between one end of the tuning
                                    network and circuit "Ground" (Common), which is also the common
                                    return for power and control signals. The "hot" output side of the
                                    matching network connects to the antenna post and the counterpoise
                                    connection (in the case of the SG-230, the stud at the bottom of the
                                    case) connects back to RF / power common via a pair of
                                    paralleled .033uF capacitors in parallel with a 220K 1W resistor.
                                    For any frequency in the range of the tuner, these paralleled
                                    capacitors amount to a dead short. This technique is clearly
                                    implemented to break the DC connection between the counterpoise and
                                    the return back to the power supply so that whatever is used as a
                                    counterpoise in the normal random-wire matching scenario can't
                                    produce sneak paths back to power ground. This is the same type of
                                    ground isolation technique that was used in the old hot-chassis
                                    transformerless tube radios and TVs from days gone by. At RF,
                                    however, the control and power lines CAN be very much a part of the
                                    RF return circuit, and therefore part of the antenna. It's never
                                    been clear to me why the SGC designers didn't complete the job of
                                    isolating the RF and power/control returns by simply putting small
                                    chokes in the non-RF lines, but they didn't.

                                    For any load connected to the output of the matching network, RF
                                    current flowing "out" the antenna port WILL flow "back" into the
                                    counterpoise port, and the majority of the return current will take
                                    whichever path presents the lowest impedance. If the tuner is being
                                    used to match a random wire it is important that the vast majority
                                    of the return side RF current be forced to find its way back to the
                                    low side of the matching network through some path that has a stable
                                    and significantly lower impedance than the power/control lines.
                                    Hence the requirement for a sizable counterpoise to insure matching
                                    stability and minimize "RF in the shack" problems.

                                    For the case of a loop or a dipole (or more properly, a doublet),
                                    which are (more or less) balanced loads across the matching network
                                    output, the current out of the antenna port will return pretty much
                                    completely in a closed loop via the other side of the feedline to
                                    the counterpoise port. Barring large amounts of pickup from the
                                    control lines being in the near field of the antenna, the control
                                    lines are essentially out of the picture as part of the RF return
                                    path. This is of course an oversimpification, as many factors can
                                    upset the balance of the antenna, but as a first-order approximation
                                    it is good enough. Feeding a doublet a small distance away from its
                                    center will neither change the current distribution on the antenna
                                    nor appreciably affect the current balance at the feed point; it
                                    just changes the feedpoint impedance. This is the principle used in
                                    the various "Windom" off-center fed designs.

                                    When feeding a doublet or loop via a length of some kind of
                                    feedline, the load the matching network has to deal with will be
                                    determined by the feedpoint impedance of the antenna as transformed
                                    through the feedline. If the matching network can be adjusted to
                                    transform the resulting complex impedance to a nominal 50 Ohms
                                    resistive at the operating frequency, the system will be happy
                                    irrespective of whether the feedpoint of a doublet is exactly at the
                                    center or not.

                                    The real question of whether or not a particular antenna will match
                                    successfully is whether the tuner is capable of matching the load
                                    the antenna system (including feedline) presents at its output
                                    terminals, not the exact geometry of the antenna. The matching range
                                    of the tuner is determined by the adjustable network constants
                                    available. Since electrically short antennas are highly capacitive
                                    loads, as a first approximation the matching capability of a lowpass
                                    tuner topology such as that used in the SGC designs for short wires
                                    can be inferred by the maximum inductance available. That's why the
                                    physically larger (and more expensive) tuners can match shorter
                                    wires at a given frequency.

                                    There are other constraints as well. Although the tuner may be
                                    capable of finding a setup that transforms a given impedance to 50
                                    Ohms, it may well be that RF currents and voltages at various points
                                    in the matching network can reach values capable of damaging its
                                    components, even at power levels well below its nominal rating. For
                                    example, if you find an autotuner trying to retune itself after a
                                    few seconds of high-duty cycle transmission, you're probably seeing
                                    the detrimental effects of RF heating in one or more of the network
                                    capacitors.

                                    The bottom line is that the design used by the SGC tuners does NOT
                                    require a particular "magical" antenna arrangement to work properly.
                                    They work just fine feeding doublets as well as end-fed wires. I
                                    have had great success feeding a 102' doublet via a length of 450
                                    Ohm ladder line. Depending on the exact geometry, it may be
                                    necessary to fool around with the feedline length to achieve a match
                                    on all desired frequencies. The SGC folks are right in discouraging
                                    the use of coax as a feedline for this kind of antenna. Coax is way
                                    too lossy at the high VSWRs that are inherent in this kind of
                                    service. Stick with a low-loss feedline and you'll find it works
                                    quite well.

                                    73...
                                    Randy, W8FN

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